1. Technical Field
The present invention relates to a terminator circuit, a test apparatus, a test head and a communication device. More particularly, the present invention relates to a terminator circuit which reduces the overshoot at the end point, and a test apparatus, a test head and a communication device including the terminator circuit.
2. Related Art
FIG. 1 shows the configuration of a conventional terminator circuit 10. The terminator circuit 10 includes therein an amplifier 18, a resistance 22, and a capacitor 24. The terminator circuit 10 has a function of reducing the overshoot of the input signal input into comparators 14 and 16 provided in a test head of a test apparatus by a device under test (hereinafter referred to as DUT) 12. Here, the input potential VCPIN input into the comparators 14 and 16 is theoretically equal to (((VDUT−Vtt)/(RDUT+Rterm))×Rterm)+Vtt.
According to the terminator circuit 10 shown in FIG. 1, the output resistance Rvtt of the amplifier 18 is finite. Therefore, if the amplifier 18 has an operating frequency range including a high frequency, and has a high gain, the influence of the output resistance Rvtt can be ignored. However, if the amplifier 18 is constituted by using a typical operational amplifier, the operating frequency of the amplifier 18 is lower than the frequency of the input signal from the DUT 12, and the output resistance Rvtt affects the input potential VCPIN input into the comparators 14 and 16. As a typical solution for this problem, the capacitor 24, which has a high capacitance Cvtt, is additionally provided between the ground potential and a point between the input ends of the comparators 14 and 16 and the output end of the amplifier 18. However, if the input signal from the DUT 12 includes a high frequency component, the conventional terminator circuit 10 can not track the input signal to sufficiently reduce the overshoot of the input signal.